1. Field of the Invention
This invention relates generally to liquid delivery systems, and is concerned in particular with the on demand mixture and constant flow delivery of multiple liquids, some of which may have elevated viscosities and/or levels of suspended solids, and others of which may require delivery at extremely high ratios.
2. Description of Related Art
As herein employed, the term “on demand” means a system in which the mixture of liquid components occurs in response to and simultaneously with delivery of the resulting mixture.
With reference to FIG. 1, a prior on demand liquid mixing and delivery system is generally depicted at 10 and includes a mixing chamber 12. A first liquid component, which may for example be water received via a conduit 13 from a municipal water source, is supplied to the mixing chamber via a first supply line 14. The first supply line includes a first constant flow valve 16, a downstream metering orifice 18 and an optional check valve 20.
As herein employed, the term “constant flow valve” means a flow control valve of the type described, for example, in any one of U.S. Pat. Nos. 7,617,839; 6,026,850 or 6,209,578, the descriptions of which are herein incorporated by reference in their entirety.
These types of valves are normally closed, are opened in response to pressures exceeding a lower threshold level, are operative at pressures between the lower threshold level and an upper threshold level to deliver liquids at a substantially constant pressures, and are again closed at pressures above the upper threshold level.
A second liquid component, e.g., a tea concentrate, is received via conduit 22 and is supplied to the mixing chamber 12 via a second supply line 24. Conduit 22 is connected to a pressurized source of the second liquid component, one non limiting example being a pump 26, which may be driven by compressed air received via conduit 27. The second supply line includes a second constant flow valve 28, a downstream second metering orifice 30 having a fixed size, and another optional check valve 32. The first and second constant flow valves 16, 28 serve to deliver the first and second liquid components to the mixing chamber 12 at substantially constant pressures, irrespective of variations in the input pressures in the conduits 13, 22 between the upper and lower threshold levels of the valves, and at substantially constant flow rates governed by the flow resistances of the first and second metering orifices 18, 30.
The first and second liquid components are combined in the mixing chamber to produce a liquid mixture having a mix ratio governed by the selected variable size of the first metering orifice 18 and the fixed size of the second metering orifice 30.
Although not shown, it will be understood that the locations of the first and second metering orifices 18, 30 may be reversed, with the adjustable metering orifice 18 being located in the second supply line 24 and the fixed metering 30 orifice being located in the first supply line 14. Alternatively, the first and second supply lines 14, 24 may both be equipped with either fixed or adjustable orifices.
A discharge line 34 leads from the mixing chamber 12 and through which the liquid mixture is delivered to an on/off dispenser 36. A third metering orifice 38 is provided in the discharge line 34. As shown, the third metering orifice is upstream and separate from the dispenser 36. Alternatively, the third metering orifice may be included as an integral component of the dispenser.
When the dispenser is open, the discharge line 34 has a maximum flow rate that is lower than the combined minimum flow rates of the first and second supply lines 14, 24, thus creating back pressures in the first and second supply lines downstream of their respective constant flow valves 16, 28. These back pressures, together with the inlet pressures applied to the constant flow valves, maintain the constant flow valves open, thereby delivering the first and second liquid components to the mixing chamber at substantially constant pressures and flow rates.
For many applications, the above described system operates in a generally satisfactory manner, although there are certain applications that can be potentially problematic. For example, when the second liquid component has an elevated viscosity and/or level of suspended solids, and the ratio of the first liquid to the second liquid is relatively high, e.g., 400:1 there is a danger that the metering orifice 30 in the second supply line 24 will become plugged, necessitating a shut down of the system while the metering orifice is either cleaned or replaced. Such maintenance procedures are both disruptive and costly.
Even when the second liquid has a relatively low viscosity and has little if any suspended solids, its mixture with the first liquid at extremely high ratios on the order of 1000:1 can be difficult if not impossible to achieve due to limitations imposed by the metering orifices.
Also, for certain liquid combinations, adequate mixture in the mixing chamber 12 may be difficult to achieve, resulting in a less than a homogeneous mixture being delivered to the dispensing valve.